Obito stated himself that he couldn't handle dual rinnegan. Check your mangafacts, bruh.
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Curse Marks are senjutsu. So chakra is involved.
Since we saw Sasuke take Itachi's eyes and the power increase his MS jutsus gained.
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Madara is a special case. His feats are not Sasuke's feats, or Itachi's, or Shisui's or Obito's.
@bold
Now that is fanfic. Naruto is an Uzumaki. Even without Kurama, he has 4x the chakra of Kakashi ( a standard kage level shinobi). Plus, you need high chakra reseves to learn sage mode.
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